Prize-Winning Lamp Design Hampered by Impossible Dynamo

Gravia_by_Clay_Moulton_300.jpg

What do you get when you cross a tech blogger with someone intelligent? Why Daniel Rutter, who has run the numbers on the Gravia Lamp concept which won second place at the Greener Gadgets competition. Turns out the gravity-powered LED lamp pretty much could never work.

22.7 kilograms falling 1.22m in gravity of 9.8 metres per second squared gives you a grand total of 271.4 joules.
That, once again ignoring losses (which are likely to be considerable, seeing as there’s a ball-screw and an electrical generator in the Gravia), will by definition run a one-watt lamp for 271.4 seconds, or four and a half minutes.
If you downgrade the lamp to one tiny 0.1-watt LED night-light, you get three-quarters of an hour.
The maximum possible luminous efficacy for any kind of lamp that will ever exist – if every quantum of energy going into the thing is used to make visible photons that come out – is 683 lumens per watt. And that’s for a lamp that emits monochromatic 555-nanometre green light, not white (the world record for white LEDs in the lab so far is less than 150lm/W), but never mind that for now.
So if your tenth-watt lamp is just such a perfect device that can never actually exist, it will emit 68.3 lumens of light.

Look at all the shiny maths! Another critic pointed out that the Gravia would either need a 4,000-kilogram mass to drop 1.5 meters to power the lamp for four hours or to extend the design’s track for its 50-pound mass to 259 meters.

In fairness, the inventor has published a retraction and will give back the $1,000 Greener Gadgets prize. And I certainly didn’t realize there was anything wrong with the design. I got about as far as “Huh, I wonder why nobody ever used such a clever weighted system before?” and never gave it any more thought. I mean, if science can invent magical pipes that whistle when you invert them, surely lamps are just a step away?

STOP PRESS: Pixie dust unsuitable for household lighting [Dan's Data]

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6 Responses to Prize-Winning Lamp Design Hampered by Impossible Dynamo

  1. semiotix says:

    Jesus, remind me never to take a class from Professor Dan. By my calculations, even with 100% perfect conversion, it should take a mass on the order of an aircraft carrier raised ten kilometers against the Earth’s gravity to generate the surplus assholery in that post. I suspect he’s surreptitiously using an external power source.

  2. bardfinn says:

    #4: Contempt of crooks while in defense of actual standards is no vice.

  3. Clif Marsiglio says:

    Good going Dan! I knew you were useful for something!

  4. morcheeba says:

    Maybe the lamp is only for use on planets with a gravity of 3800 m/s^2?

  5. strider_mt2k says:

    They broke the upside-down whistling tube barrier?

    These are the days of miracle and wonder…

  6. FoetusNail says:

    Didn’t morcheeba’s math skilz beat this guy Dan to the punch by about two weeks, 15 mins after Mark’s original post, while also not being like a total prick? I think I’ll continus to read the comments of boing boing readers.

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